Method and apparatus for mass analysis of samples

ABSTRACT

The present invention comprises an apparatus and a method for mass analyses of an array of samples contained in distinct sample holders. The sample holders are placed on a plurality of sensors which preferably comprise an array of microbalances providing output signals comprising mass data on the array of samples.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of copending application Ser. No.10/883,594 filed Jul. 1, 2004, the contents of which are herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the simultaneous measurement of massproperties of an array of samples. More specifically, the inventionrelates to the determination of the mass in the μg to gram range, butalso in ranges higher or lower, of an array of samples.

BACKGROUND OF THE INVENTION

Gravimetric measurements at the laboratory scale have been hampered byrelatively ponderous equipment and inefficient measurement speeds. Thereis a need for more efficient methods of monitoring and recording themass of a number of materials in order to evaluate the properties ofand/or screen and select optimum candidates for further development.

The optimization of materials for use in such applications as catalystsand adsorbents requires characterization of a large number of samples ofsuch materials often as rapidly as possible. Analytical techniques forsuch characterization must be fast as well as accurate to deal with thelarge amount of data associated with the optimization. Parallel ratherthan serial measurement would facilitate rapid generation of data forsuch characterization. These measurements are particularly useful in thedetermination of properties or performance of, for example, surfaceproperties such as surface area and pore diameter, which are indicatorsof potential performance in a variety of applications.

Micromachining technologies have become widely available in the pastdecade. Silicon micromachining in particular enables full integration ofmechanical and sensing elements, offering cost effective production ofsmall transducers with the potential of producing an array of sensors asa single integral unit.

Publication US 2002/0028456 A1 discloses a sensor array disposed on asubstrate to measure various material properties of samples deposited onthe substrate. Samples may be deposited on the sensor in solution or byvapor deposition. Properties, which can be measured, includetemperature, heat capacity, thermal conductivity, thermal stability,dielectric constant, viscosity, density, elasticity, capacitance andmagnetic properties.

WO 00/20850 teaches a multi-sensor device for gravimetric chemicalmeasurements of gaseous or vapor-state analytes comprising a substrateand a plurality of sensors made from piezoelectric elements realizedwith thick-film technology on the substrate. The sensors are coated withsensitive coatings for absorbing the analytes.

U.S. Pat. No. 5,983,711 discloses a temperature-controlled gravimetricmoisture analyzer comprising a sample holder attached to a weighingmechanism, a temperature sensor and a heater and controller respondingto the output signal of the temperature sensor. This patent does notdisclose an array of weighing devices, however.

WO 03/071241 discloses a spring scale for micro-weighing comprising aload platform suspended by at least three flexural springs in asurrounding frame, with bridge-connected strain gauges for measuringstrain on one side of the flexural springs. There is no suggestion of anarray of weighing devices, however.

U.S. Pat. No. 4,566,326 teaches an automatic adsorption and desorptionanalyzer for performing measurements on a plurality of powder samplesusing a plurality of sample cells with associated valves, controls andsensors. The analyzer can measure surface area, total pore volume,micropore volume, average pore radius, and pore-size and surface-areadistributions substantially simultaneously on a plurality of samples.This analyzer represents known art in accomplishing the purposes of thepresent invention.

The art does not suggest, however, either an apparatus or a method foreffecting mass analyses on an array of samples contained in distinctsample holders.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and a method for massanalysis of each of an array of samples contained in an array ofdistinct sample holders positioned to interact with a plurality ofsensors providing output signals comprising mass data on the array ofsamples. Through such analyses, the invention enables the rapiddetermination of a variety of properties of the samples related to theirmass. Subsequent analyses of further arrays of samples also areexpedited.

In a more specific embodiment, the invention provides an apparatus formass analyses of each of an array of samples comprising an array ofdistinct sample holders containing the samples positioned to interactwith a plurality of microbalances providing output signals comprisingmass data on the array of samples.

In a yet more specific embodiment, the invention provides an apparatusfor mass analyses of each of an array of samples comprising an array ofdistinct sample holders containing the samples positioned to interactwith a plurality of spring scales providing output signals comprisingmass data on the array of samples.

In another specific embodiment, the invention provides an apparatus formass analyses of each of an array of samples comprising an array ofbaskets containing the samples positioned to interact with a pluralityof microbalances providing output signals comprising mass data on thearray of samples.

In an alternative embodiment, the invention provides a method for massanalysis of an array of samples by placing the array in an array ofdistinct sample holders, positioning the sample holders to interact witha plurality of sensors providing output signals comprising mass data onthe array of samples, and determining the mass of each of the samplesfrom the output signals.

In a more specific alternative embodiment, the invention provides amethod for mass analysis of a multitude of samples by placing thesamples in an array of distinct sample holders, positioning the sampleholders to interact with a plurality of sensors providing first outputsignals comprising mass data on the array of samples, subsequentlyexposing the array of samples to a change in environmental conditions,subsequently measuring second output signals from the array of samples,and determining one or more properties of each of the samples bycomparing the output signals from the array of samples before and afterthe change in environmental conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. I illustrates a broad embodiment of the apparatus of the inventioncomprising a small array of six sample holders interacting with aplurality of the same number of sensors.

FIG. II illustrates the apparatus of the invention in an embodimentcomprising a spring scale in an element of an array.

FIG. III shows an example of a bridge circuit that can be used in massanalysis.

FIG. IV is a cross-sectional side-view illustration of a spring scaleconnected to a base part.

FIG. V illustrates the apparatus of the invention in an embodimentcomprising a suspended basket in an element of an array.

FIGS. VI-A and VI-B illustrate an alternative arrangement of themicrobalance as a cantilever.

DETAILED DESCRIPTION OF THE INVENTION

In summary, the present invention provides an apparatus and a method formass analysis of each of an array of samples contained in an array ofdistinct sample holders positioned to interact with a plurality ofsensors providing output signals comprising mass data on the array ofsamples. Although elements of the method and associated apparatus aredescribed in the singular, it is to be understood that two or moreparallel or series sets of each element or of the entire apparatus arewithin the scope of the invention.

The “array” of samples and sample holders encompasses at least four (4),more usually six (6) or more, generally at least eight (8), andoptionally forty-eight (48) or more samples and holders. It is withinthe scope of the invention that some multiple of these numbers iscontained in the array such as 24, 96, 392, or 1264 arranged in arow-and-column formation similar to that of a microtiter tray.Preferably the sample holders are spatially separated such thatindividual members of the array are addressable separately. The“plurality” of sensors is within the same numerical ranges as describedfor the “array,” and preferably the number of sensors is the same as thenumber of samples and sample holders. Considering the invention inrelation to the known art using parallel or sequential analysis, theequipment and/or time required for analyses according to the known artwould be relatively expensive.

By “sample” is meant a substrate for which mass analysis is desired.These substrates are often solids, but not necessarily limited to solidmaterials, for example liquids, gels, slurries, and the like. Possibleexamples of liquid applications are with respect to ionic liquids,monitoring gas solubility in liquids, etc. Possible examples of solidsamples comprise, without limiting the invention, ceramics, molecularsieves, other inorganic compounds, composites, metals and metal alloys,intermetallics, carbon, ionic solids, molecular solids, covalent networksolids, organometallic materials, organic polymers and combinationsthereof. Substances for which surface properties are important arepreferred, and especially preferred substances comprise metal oxides,molecular sieves and catalytic agents.

Sample form is not critical to the definition of the invention. If asolid materials, the sample may be a single solid monolith, or asparticles, films, plates, discs, beads, spheres, rods, wires, or anyform suitable for the analysis to be conducted. Preferably the solidsample is in the form of particulates, and a fine-powder form of sampleis especially preferred. In a fine powder, the average particle sizetypically will range from about 0.01 μm to about 1000 μm, and moreusually will be between about 0.1 μm to about 100 μm.

The present invention comprises an array of sample holders, with asample holder or container provided for each sample to be analyzed. Thesample holder may be any device which can contain a sample and which istransferable to and from a sensor to be defined hereinafter. Preferablythe sample holder or container provides a concave surface facing upwardwhich contains the sample without risk of substantial spillage. Suitableconfigurations comprise, without limitation, pans, cups, saucers,plates, indentations and depressions. Alternatively, the sample holdermay comprise a basket which is supported on a sensor by a hook, loop,ring, clip, clasp or other fastener. Advantages of placing the sample ina sample holder to be transferred to and from a sensor include:

avoidance of sensor contamination by direct contact with the sample, and

the ability to effect measurements in parallel with the handling ofsamples, and cleaning of sample holders through multiple sets of sampleholders.

Any material that does not adversely affect results of the analysis issuitable for the sample holder. Preferably the surface of the sampleholder that contacts the sample is stable and inert to the sample at allconditions of the method of the analysis. One or both of ceramic andmetal materials are especially preferred for the sample holders.

Optionally, input to the analysis is provided through the sample holder.For example, without limitation, the sample holder may comprise athermally conductive material through which heat may be provided to thesample or the temperature of the sample measured. Alternatively,electrical energy may be transmitted to the sample through the sampleholder. It is within the scope of the invention that the sample holderis coated or layered with material that aids in the analysis throughphysical or chemical action. Further, the sample itself could be coatedonto the surface of the sample holder through chemical or physicalbonding, evaporation and the like.

Following the analyses of the array of samples, each analyzed sample maybe unloaded from the respective sample holder and a fresh array ofsamples then is placed on the array of sample holders. Preferably one ormore additional arrays of samples on additional sample holders have beenprepared while the analyses are being effected such that the additionalarray of samples may be positioned to interact with the plurality ofsensors while the analyzed samples are being unloaded from theirrespective sample holders. Optimally, the array of sample holders iscontained in a tray which may be lowered toward the apparatus comprisingsensors to place the sample holders in position on the sensors. In thismanner, the preparation and unloading of samples will not delay theanalysis of samples, and the apparatus comprising sensors is utilizedmore effectively.

FIG. I illustrates an array of six distinct sample holders 1 positionedto interact with a plurality of six sensors 2 providing output signalscomprising mass data on the array of samples. The sensors comprisespring scales contained in a frame 3 as described hereinbelow for oneindividual unit of the six sample holders and spring scales. Asdiscussed hereinabove, the “array” or “plurality” comprises at least 4such units, and preferably a larger number of units.

Suitable sensors include any type that can measure mass changes andsupport a sample holder. Sensor materials comprise one or more ofmetals, silicon, other semiconductor materials, glasses, carbon,polymers, membranes and the like, with semiconductor materials such assilicon being particularly favored. Preferred sensors of the inventioncomprise microbalances, in particular spring scales as described inInternational Publication WO 03/071241 which is incorporated herein inits entirety by reference thereto. The preferred spring scale comprisesa load platform suspended in a surrounding frame by means of at leastthree flexural springs, with bridge-connected strain gauges arranged formeasuring strain on one side of the flexural springs.

FIG. II shows a preferred embodiment of the invention schematically in aview from above. A spring scale, in this example having the shape of asquare, has in its center a load platform 1 upon which the sample holderas shown in FIG. I is placed. The load platform 1 is suspended in aframe 2 by means of flexural beams or flexural springs 3, whichbeams/springs are in the shown example arranged along each side edge ofthe load platform, and slits 5 and 6 have been etched or machined toprovide the flexural beams 3 in such a manner that a slit has one slitpart 5 on the outside of the flexural beam 3 and a continuing part 6 onthe inside of the next flexural beam 3. In such a construction theflexural beams 3 become relatively long and compliant, i. e. the loadplatform 1 can be given a deep swing. Each flexural beam 3 is situatedin a gap between the frame 2 and the load platform 1, which gap isdefined by the slit parts 5 and 6. Each flexural beam 3 has anattachment spot 7 to the load platform 1 situated directly opposite theattachment spot 8 of an adjacent flexural beam to frame 2. Reference 4designates sensors for recording a load on the load platform 1. When asample holder is placed on the load platform 1, the platform will sinkin a direction away from the observer, and the flexural beams 3 willbend and assume a shape similar to a shallow S. The load platform willthen at the same time rotate somewhat about an axis perpendicularly tothe plane of the load platform, as the length of the beams 3 remainsubstantially constant.

With the above-mentioned S-shape in the flexural beams 3 when theplatform is loaded, the most intense mechanical stresses in the beamsare found in the crossing areas to frame 2 and load platform 1 (i. e. atthe attachment spots 7 and 8). It is therefore favorable to mount straingauges 4 for example as shown in FIG. II. Alternatively, the straingauges can be mounted in the crossings to the load platform instead ofcrossings to the frame, but this will require longer leads from thestrain gauges and to the signal processing equipment. In the way thestrain gauges 4 have been mounted in FIG. II, all four gauges arepositioned in the same direction in order to optimize connecting thesensors in a Wheatstone bridge. The sensors/gauges can alternatively bemounted in different directions; for example turning two of them 90°relative to the other two with modification of the bridge connection.

The strain gauges 4 can be arranged as separate sensors on top of thecrossings in question (attachment spots 8 or 7), by means of depositingand pattern forming, or by gluing ready resistors. Alternatively, straingauges in the form of piezo-resistors can be manufactured as an integralpart of a favored silicon structure or arranged as a surface element inany suitable manner.

In a favorable embodiment of the invention the load platform, flexuralsprings and frame are shaped as one micro-machined or etched piece ofsemiconductor material; optimally this material is silicon. The straingauges, preferably piezo-resistive resistors arranged on a crossingbetween the flexural spring and the frame or load platform, may beintegral in the piece of the solid material. The semiconductor material,primarily for shaping the spring scale, thus also may be applied toshaping the sensor elements used for detecting a load.

FIG. III shows an example of a bridge circuit that can be used forproviding a mass analysis by means of the scale of the presentinvention. The bridge circuit shown is a Wheatstone bridge adapted tothe case of FIG. II, in which every strain gauge 4 is mounted in thesame direction. The strain gauges are in the form of resistors 4, andthe Wheatstone bridge circuit is completed by a current source (battery)11 and a measurement instrument 12. This is a standard type circuit, butother bridge circuit variants may be used in connection with otherembodiments with other strain gauge configurations.

In a broad embodiment, the spring scale according to the invention isnot restricted to a single piece or from semiconductor material.Further, many geometrical shapes may be used as long as the central loadplatform is suspended by at least three flexural springs that connectthe load platform with a surrounding frame.

One alternative embodiment is a substantially circular load platforminside a circular opening in a frame. Curved flexural beams or springsare attached to the load platform and frame respectively. Usually theattachment spots are situated directly opposite each other, but they mayoverlap or even spiraling past/along each other in the gap between theload platform and the frame. Strain gauges as before are situated at theflexural beam attachment spots to the frame or platform, i. e. at thespots where surface stress is at the most intense in a weighingoperation.

Another possible configuration comprises a triangular load platform andthree flexural beams between the load platform and the frame. Straingauges, mounted for instance in the three attachment spots can beconnected in a modified bridge connection. Thus, a plurality ofgeometrical shapes will satisfy the requirements of the invention.

A construction with four flexural springs is preferable, for at leastthree reasons:

-   1. In a Wheatstone bridge of standard type, just four resistors are    included.-   2. To have a stable load platform, one should not use too many    beams.-   3. For a micro-scale manufactured in silicon, it is a point that    silicon (100) wafers have four-fold symmetry and this entails that    the piezo-resistors should be positioned along the [011] or [011]    directions.

FIG. IV shows schematically a cross-section through a central part of aspring scale comprising a platform 1 upon which a sample holder has beenplaced in accordance with the FIG. I embodiment of the presentinvention. The central area comprising the platform is thinned downrelative to the frame area 2 which may be substantially thicker. Theflexural beams 3 appear such that two beams can be seen in a side viewand exhibit an S-shape.

The embodiment shown in FIG. IV also shows an optional base part 4 whichcan be made of glass and attached to the frame 2 by means of anodicbonding. By making the base part 4 extend in under the load platform 1,it forms a swing-down limit for load platform 1 as a safety function forthe flexural springs 3. As shown, the base part 4 is also may beequipped with a central opening 5 for regard to inspection and cleaning.Above the scale, an optional roof 6 may be provided as an end stop asprotection and for possible swings upward for load platform 1.Optimally, there is a central opening 7 in the roof in order that anobject to be weighed can be laid down on the load platform. The roof maybe glass and fixed to the silicon structure 8. Reference 9 designates acontact section for signal leads from the strain gauges. The roof may beglass and fixed to the base part 4.

In an alternative embodiment, the sample holder is placed on amicrobalance as a hanging basket. An example of this embodiment isillustrated in FIG. V. A support 1 comprises an array of microbalances,one microbalance 2 being shown in the Figure. A sample holder 3 issuspended as a hanging basket from the microbalance via a loop 4attached to the microbalance and a wire 5 from the loop to the basket.In this embodiment, the hanging basket and sample holder, attachment tothe microbalance, and means for connecting the attachment and hangingbasket may be any of those known in the art which can contain the sampleand remain stable under the conditions of the mass analysis.

Although it is preferred that the mass analysis be conducted usingstrain gauges, and particularly piezoresistors in a Wheatstone bridge asdescribed hereinabove, it is within the scope of the invention thatother methods of detecting the deflection of the microbalance may beused. These methods include but are not limited to the use of optical ormagnetic detectors. In one embodiment, deflection signals from each ofthe microbalances are determined using a photodetector.

In yet another alternative embodiment, the microbalance comprises acantilever; two examples are identified in FIGS. VI and VII. In FIGS.VI-A and VI-B, a cantilever 1 comprises a ring configuration 2 forsuspending a sample holder 3 which preferably is a hanging basket. Thebasket is attached to the ring 2 of the cantilever by any suitablemeans, preferably via a wire 4. The bridge 5 of the cantilever comprisesstrain gauges 6 and 7 in the form of piezoresistors to effect the massanalysis of a sample placed in the sample holder 3.

In FIGS. VII-A and VII-B, a cantilever 11 comprises a slingconfiguration 12 for suspending a sample holder 13 which preferably is ahanging basket. The basket is attached to the sling 12 of the cantileverby any suitable means, preferably via a wire 14. The bridge 15 of thecantilever comprises strain gauges 16 and 17 in the form ofpiezoresistors to effect the mass analysis of a sample placed in thesample holder 13.

Signals from the microbalances are read through a readout board andprocessed by a microcomputer. A temperature signal can be used tocompensate for temperature dependence of the sensor. The temperaturesignal can be provided from a separate resistor or diode, or one canmonitor the total bridge resistance.

In measurements were the sample is heated or cooled, thermoelectricvoltages at junctions can affect the measurements. This can becompensated by periodically switching off the power source (11) andsubtracting the output from the measurements. One can also use acompound AC excitation and a lock-in measurement.

The computer is equipped with suitable software for designing the test,controlling the environment, and acquiring and analyzing data todetermine the properties of the samples.

Preferably the mass analysis is effected in a controlled environment.The environment can be controlled when the samples and sample holdersare placed within one or more suitable sealable chambers which isolatethe sample holders from uncontrolled environmental conditions.Environmental conditions to be controlled comprise, without limitation,pressure, temperature and fluid composition, for example but not limitedto gases surrounding the samples and sample holders. Suitable pressurescomprise between about 10⁻¹⁰ Torr to 300 bar, and preferably from about10⁻⁶ Torr to 150 bar; temperatures generally are in the range of about−200° to about 1000° C., and more usually less than about 500° C. Anysuitable heating or cooling device known in the art may be used tocontrol the temperature.

The composition of the fluid medium in the controlled environment may bevaried for weighing the samples and to effect tests describedhereinafter. In the case of the fluid medium, suitable gases includewithout limitation one or more of nitrogen; carbon monoxide; carbondioxide; ammonia; SF₆; argon, helium or other inert gases; and butane,pentane or other hydrocarbons.

Often environmental conditions are varied over time in order todetermine sample properties as described hereinbelow. The variation maycomprise one or more of a substantial change in temperature, a change inpressure, and a change in compositional environment. For example, one ormore properties may be determined by the steps of measuring first outputsignals from the array of samples, subsequently exposing the array ofsamples to a change in environmental conditions, subsequently measuringsecond output signals from the array of samples, and determining one ormore properties of each of the samples by comparing the first and secondoutput signals. The steps may be repeated on the tested samples throughsequences of subsequently exposing the array of tested samples to afurther change in environmental conditions, subsequently measuringfurther output signals from the array of samples, and determining one ormore properties of each of the samples by comparing the output signalsfrom the further testing. The deflection signals of the array ofmicrobalances can be compared before and after the change inenvironmental conditions. Preferably this is effected using a knownsensor curve for each of the plurality of spring scales.

Mass also can be measured by recording the eigenfrequency of the loadedbalance and relating this according to the equation ω=√{square root over(k/m)} where k is the spring stiffness, and m is the effective mass. Thevibrations can be induced by external agitation of the whole arrayfollowed by monitoring the free oscillations of each balance. The methodcan be used for calibration, or measurements when large offsets aresuperimposed on the transducer output (e.g. by thermoelectric effects).

Uses

The microbalance of the invention could have one or more of a variety ofuses in addition to sample weighing. For example, monitoring weightchanges in samples due to changes in environment or as function of timecan yield data on surface area, pore size and volume, acidity/basicityand metal function among other characteristics. Changes in theenvironment due to mass changes in the samples can be monitored, and themicrobalance can be used for reactivity testing.

The microbalance array by itself could be used to weigh samples for asample array. This function could be used as a preparation step foranother operation, for example characterization analysis, reactivitytest, or synthesis. Also the weight change alone could be a key part ofan analysis involving exposure of a set of samples to a specific set ofconditions (e.g. coke deposition for a reactivity test, hydrogen uptakeat high pressure). Other possible uses include, without limitation:

Isotherms from Physisorbed Probe Molecules:

Surface Area

-   -   Either the Langmuir equation (single layer adsorption) or the        BET (Brunauer, Emmett, and Teller) equation (multi-layer        adsorption) or any other appropriate method of determining or        calculating is used to derive a surface area from isotherm data.        Typically nitrogen is used as the adsorbate.

Pore Volume

-   -   Using the Kelvin Equation, the amount of adsorbate is expressed        as a corresponding volume of pores.

Pore Size Distribution

-   -   Typically the desorption isotherm along with the Kelvin Equation        is combined with various ways to estimate an adsorbate film        thickness as a function of its partial pressure. These equations        are used to estimate the distribution of pore sizes for a        sample.

Adsorption Capacity

-   -   For a given set of conditions (vapor pressure and temperature),        the amount of probe molecule adsorbed is measured. This value is        of interest for evaluating or comparing materials. Typical        examples are selective adsorption and gas-storage applications.        Also of interest is the adsorption capacity for a single        adsorbent using a set of probe molecules of various kinetic        diameters. This is analogous to McBain measurements, and helps        to classify the pore size of a material.

Adsorption Kinetics (Diffusion)

-   -   By measuring the uptake rate of a probe gas, an estimate of the        diffusion constant for the adsorbent/adsorbate system can be        made. When made at a range of temperatures, this method can be        used to determine an activation energy for diffusion.

Heats of Adsorption

-   -   Measurement the adsorption capacity at several temperatures        allows for calculating the heat of adsorption for a given sample        and adsorbate.        Isotherms from Chemisorbed Probe Molecules

Acidity

-   -   The amount of a probe base adsorbed by a sample can be used to        estimate the number of acid sites for the sample. By making        either adsorption measurements at several temperatures, or by        measuring the amount of base desorbed as a function of        temperature, the acid strength distribution for a sample can be        estimated.

Example Probe Molecules: NH₃, CO, Pyridine, Trimethylphosphine

-   -   Number of Acid Sites    -   Strength of Acid Sites

Basicity

-   -   Similar to acidity, but using probe molecules to characterize        basicity.

Example Probe Molecules: Ethene, Propene, 1-Butene

-   -   Number of Basic Sites    -   Strength of Basic Sites

Metal Function

By selecting the appropriate probe molecule, the metal or metals loadedon a sample can be characterized. If the amount of metal loaded on thesample is unknown, the amount of a probe molecule adsorbed by materialscontaining a metal function can be used to determine the amount ofexposed metal atoms. If the metal loading is known, this sameinformation can be used to determine what percentage of the metal isaccessible for catalytic reactions. This type of information would bevery useful to characterize the metal dispersion as a function ofimpregnation conditions, secondary treatments (e.g. hydrothermal), anddeactivation due to carbon deposition.

Mass changes in samples due to redox of metals on a sample can also beused to characterize metal content, dispersion, and activity.

-   -   CO Uptake    -   H₂S Uptake    -   H₂/O₂ Redox/Uptake        Atmospheric Sampling

A set of materials could be placed in the microbalance array, andexposed to a process stream or gas from the surrounding environment inorder to characterize the process stream or gas. One example would be toselect a set of microporous materials covering a range of pore sizes.Each unique material would only adsorb molecules in a specific sizerange. By simultaneously comparing the amount adsorbed for eachmaterial, the gas stream can be characterized.

Likewise, materials containing specific cations that are known to changeadsorption properties could also be used to characterize a gas stream.

Reaction Pulse Experiments

Coking

-   -   A reactant stream can be pulsed over a set of samples, and the        amount of carbon deposited for a given pulse can be measured.        This provides information about the reactivity, and deactivation        rate for a set of samples.

Redox

-   -   Exposing a set of samples to an oxidizing and/or a reducing        environment while measuring weight changes gives information        about redox activity and capacity. This would be similar to the        metals test mention above.

Polymerization

-   -   Information about activity and kinetics of polymerization        catalysts or initiators can be estimated by exposing such        materials to an oligomerizable or polymerizable gas.        Combined Techniques

The combination of two or more techniques for in situ analysis ofproperties of an array of samples would be a particularly valuablefeature of the present invention.

IR Thermography+Microbalance Measurement

-   -   The microbalance measurement could be combined with IR        thermography measurements. In this experiment a base (or acid)        is introduced to the sample array. During the exposure, the        microbalance would be monitoring the weight changes, and the IR        camera would be monitoring the heat changes and heat of        adsorption. The use of both techniques simultaneously provides        much more information than each technique being run        independently. The information from both measurements can be        combined to determine the number and strength of acid (or base)        sites in a material.        -   Acidity        -   Basicity        -   Reactivity

Temperature+Microbalance Measurement

-   -   By monitoring the weight changes as a function of temperature,        the system could function as a combi-tga (thermo-gravimetric        analysis). One could monitor phenomena such as water desorption        as a function of temperature, template oxidation for zeolites        (passing air during the temperature ramp), carbon burn kinetics        for regeneration studies.

XRD+Microbalance Measurement

-   -   The microbalance measurement could be combined with a combi-xrd        (x-ray diffraction) measurement. A set of samples could be        exposed to a probe gas in this system which would allow        structural information to be measured as a function of the        amount of probe gas adsorbed. Some example uses could be:        -   Impact of water on unit cell size        -   Impact of a given hydrocarbon on unit cell size        -   Impact of carbon (coke) on unit cell size (in-situ coke            burring)

The above description and examples are intended to be illustrative ofthe invention without limiting its scope. The skilled routineer willreadily understand how to extrapolate parameters of the disclosure toother embodiments of the invention. The invention is limited only by theclaims set forth herein.

1. A method for mass analysis of each of an array of samples comprisingthe steps of: (a) placing the array of samples in an array of distinctsample holders; (b) positioning the distinct sample holders to interactwith a plurality of sensors providing output signals comprising massdata on the array of samples; and, (c) determining the mass of each ofthe samples from the output signals.
 2. The method of claim 1 comprisingcalculating the mass of each of the samples substantiallysimultaneously.
 3. The method of claim 1 further comprising deriving thetemperature of each of the samples in step (c).
 4. The method of claim 1wherein the plurality of sensors comprises an array of microbalances. 5.The method of claim 4 wherein the array of microbalances comprises anarray of spring scales.
 6. The method of claim 5 wherein each of thespring scales comprises a load platform suspended by one or moreflexural springs each having a bridge-connected strain gauge arrangedfor measuring strain on one side of each of the one or more flexuralsprings.
 7. The method of claim 4 wherein the plurality of sensorscomprises one or more optical detectors.
 8. The method of claim 1wherein the one or more properties are determined by the steps of: (a)measuring first output signals from the array of samples; (b)subsequently exposing the array of samples to a change in environmentalconditions; (c) subsequently measuring second output signals from thearray of samples; and, (d) determining one or more properties of each ofthe samples by comparing the output signals from steps (a) and (c). 9.The method of claim 8 further comprising one or more repeated sequencesof steps of: (b′) subsequently exposing the array of samples from step(c) to a further change in environmental conditions; (c′) subsequentlymeasuring further output signals from the array of samples; and, (d′)determining one or more properties of each of the samples by comparingthe output signals from steps (c) and (c′).
 10. The method of claim 8wherein the one or more properties comprise at least one physisorptionproperty.
 11. The method of claim 10 wherein the one or more propertiescomprises at least one of surface area, pore volume, pore gauge, andpore-size distribution of the array of samples.
 12. The method of claim8 wherein the one or more properties comprise at least one chemisorptionproperty.
 13. The method of claim 8 wherein the change in environmentalconditions comprises a change in partial pressure of an adsorbing gas.14. The method of claim 8 wherein the change in environmental conditionscomprises one or more of a substantial change in temperature, a changein pressure, and a change in molecular environment.
 15. The method ofclaim 8 wherein the one or more properties is determined by: (a)measuring first deflection signals from the array of samples; (b)subsequently exposing the array of samples to a change in environmentalconditions to provide an array of modified samples; (c) measuring seconddeflection signals from the array of samples; and, (d) determining theone or more properties by comparing the deflection signals in steps (a)and (c).
 16. The method of claim 15 wherein the plurality of sensorscomprises an array of microbalances.
 17. The method of claim 16 whereinthe array of microbalances comprises an array of spring scales and theone or more properties are calculated by comparing first and seconddeflection signals from each of the samples during steps (a) and (c).18. The method of claim 17 wherein the first and second deflectionsignals from each of the samples are compared using a known sensor curvefor each of the spring scales.
 19. The method of claim 15 wherein thefirst and second deflection signals from each of the samples arecompared using a photodetector.
 20. The method of claim 15 wherein thefirst and second deflection signals from each of the samples arecompared using a compound alternating-current signal generator andfilter with a lock-in amplifier for detection of a deflection signal atan encoding frequency.
 21. The method of claim 5 wherein mass ismeasured by recording the eigenfrequency of the loaded balance andrelating this according to the equation Ω=√{square root over (k/m)}where k is the spring stifffiess and m is the effective mass.